C1–C2 Pedicle Screw Fixation for Adolescent with Os Odontoideum Associated Atlantoaxial Dislocation and a Compound Reduction Technique for Irreducible Atlantoaxial Dislocation
Os odontoideum (OO) is a rare congenital anomaly of the second cervical vertebra, characterized by an independent ossicle separated from the base of the odontoid process. This condition often leads to atlantoaxial dislocation (AAD), which can result in significant neurological and functional impairments. Adolescents, in particular, are at a higher risk due to their immature bones and the physical impacts they encounter in daily life. Surgical intervention is often necessary to stabilize the atlantoaxial joint and prevent further complications. This article discusses the use of C1–C2 pedicle screw fixation for treating OO-associated AAD in adolescents and introduces a novel compound reduction technique for irreducible atlantoaxial dislocation (IrAAD).
Background and Clinical Significance
The atlantoaxial joint, located between the first (C1) and second (C2) cervical vertebrae, is crucial for head rotation and stability. OO can lead to instability in this joint, resulting in AAD. In adolescents, this instability is particularly concerning due to their active lifestyles and the potential for repeated spinal cord injuries. Symptoms may include neck pain, torticollis, and neurological deficits. Without treatment, OO-associated AAD can lead to severe spinal cord compression and long-term disability.
Posterior screw-rod fixation systems have become a standard treatment for OO-associated AAD. These systems provide three-dimensional fixation, enabling effective correction and bone fusion. However, in cases of IrAAD, where the dislocation cannot be reduced through pre-operative skull traction, additional surgical techniques are required. Traditional approaches often involve transoral decompression followed by posterior stabilization, but these methods carry risks such as infection and increased hospitalization costs.
Study Design and Patient Population
This study retrospectively reviewed the medical records of 15 adolescent patients (11–18 years old, mean age 13 years; nine males, six females) diagnosed with OO-associated AAD. These patients were treated at the Department of Orthopaedic Surgery, Spine Center, Changzheng Hospital, Second Military Medical University, Shanghai, China, between January 2014 and September 2016. All patients underwent pre-operative evaluations, including X-rays, computerized tomography (CT) scans, and magnetic resonance imaging (MRI), to assess bone anatomy, vertebral artery course, and spinal cord compression.
Six radiographic parameters were measured to evaluate the instability of the atlantoaxial joint: the inner diameter of the atlantal ring (Datl), the smallest diameter of the spinal canal (Dmin), the maximum distance (Dmax), the atlantodens interval (ADI), the instability index, and the cervicomedullary angle (CMA). The instability index was calculated as (Dmax – Dmin) / Dmax * 100%, while the CMA reflected the degree of cervical spinal cord compression.
Pre-operative Management
All patients underwent pre-operative skull traction (3–5 kg for 1–2 weeks) to attempt reduction of the C1–C2 dislocation. Radiographs were obtained to assess the effectiveness of the traction. Eleven patients achieved satisfactory reduction, while four patients exhibited no reduction, indicating IrAAD.
Surgical Technique
Under general anesthesia, patients were placed in a prone position with persistent skull traction (1/12 of the body weight). A standard posterior midline incision was made from the occiput to the C3 junction. The lateral capsule of the atlantoaxial facet joint was released, and any scars or osteophytes were removed using a high-speed burr until mobility between C1 and C2 could be achieved.
C1 and C2 pedicle screws were implanted as described by Harm et al. For patients with IrAAD, a novel direct posterior compound reduction technique was employed. The rod was first fastened over the C2 screw head, and the C1 and C2 screws were detracted to loosen the joint. The base of the C2 spinous process was pushed ventrally, and the C2 vertebral body was pulled forward and downward using the lever principle. In cases of rotational dislocation, differential force was applied on the right and left sides to correct the rotational component. The rod was then fastened in its final position, and the C1 screws were pulled up using a squeeze-down device to achieve proper antero-posterior realignment of the C1 and C2 vertebrae.
Following reduction and fixation, an H-shaped autologous iliac crest graft was placed between the posterior arches of the C1 and C2 vertebrae to promote bone fusion. All operations were performed under intra-operative neurophysiological monitoring to ensure safety.
Post-operative Outcomes
All 15 patients achieved satisfactory reduction of the C1–C2 dislocation after surgery. The four patients with IrAAD who failed pre-operative traction successfully underwent the direct posterior compound reduction technique. The pre-operative instability index ranged from 39% to 88.5% (mean 51.2 ± 13.3%). No complications such as infection, cerebrospinal fluid leakage, neurological injury, vascular injury, or re-dislocation were observed.
Follow-up radiographs were obtained over 24 to 48 months. The mean time for C1–C2 bony fusion was 3.6 months. Post-operative X-rays showed significant improvement in cervical alignment, with the mean C2–C7 Cobb angle changing from 25.3° ± 12.2° to 16.7° ± 7.5°. Post-operative CT scans confirmed satisfactory placement of all pedicle screws, and MRI demonstrated improved CMA values from 134.6° ± 8.2° to 152.1° ± 7.2°, indicating sufficient decompression of the spinal cord.
The ADI remained relatively unchanged (1.39 ± 0.70 pre-operatively vs. 1.38 ± 0.69 post-operatively), while the Datl showed no significant difference (16.8 ± 2.2 pre-operatively vs. 16.97 ± 2.49 post-operatively). However, significant improvement was observed in the Dmin values, which increased from 9.84 ± 5.03 to 15.45 ± 2.19.
Clinical Improvement
All patients showed clinical improvement post-operatively. The mean Japanese Orthopedic Association (JOA) scores improved from 10.9 ± 2.0 pre-operatively to 14.5 ± 2.0 post-operatively, while the mean Neck Disability Index (NDI) scores decreased from 17.0 ± 7.5 to 9.6 ± 3.9. These results indicate significant functional and neurological recovery following surgery.
Discussion
Adolescents with OO-associated AAD present unique challenges due to their immature bones and active lifestyles. However, the craniovertebral region typically reaches adult size by 8 to 10 years of age, allowing for the use of C1–C2 screw-rod constructs in young patients. Studies have shown that posterior C1–C2 screw fixation does not significantly limit atlantoaxial growth in children over 6 years of age, making it a viable option for adolescent patients.
The direct posterior compound reduction technique introduced in this study offers a simple and effective alternative to traditional transoral decompression for IrAAD. By combining intra-operative skull traction, detracting the C1–C2 pedicle screws, and applying differential force to correct rotational dislocation, this technique achieves satisfactory realignment without the risks associated with transoral procedures.
Conclusion
C1–C2 pedicle screw fixation is an effective treatment for adolescent patients with OO-associated AAD, providing stable fixation and promoting bone fusion. The direct posterior compound reduction technique offers a viable alternative for patients with IrAAD, achieving satisfactory realignment without the need for transoral decompression. This study demonstrates the safety and efficacy of these techniques, highlighting their potential for improving outcomes in adolescent patients with complex atlantoaxial dislocations.
doi.org/10.1097/CM9.0000000000000224
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